The high-speed Ethernet (registered trademark) specifications (100BASE-X) that enable a communication speed of up to 100 Mbps include 100BASE-TX using twisted-pair cables and 100BASE-FX using optical fibers. 100BASE-FX is a full-duplex (fixed) interface, defined by IEEE 802.3, with a transmission speed of 100 Mbps using optical fibers.
A typical configuration for connecting communication apparatuses (e.g., data terminal equipment (DTE)), provided with 100BASE-TX interfaces, using an optical fiber is as follows. That is, referring to FIG. 7, connection is realized using media converters for signal-form conversion between 100BASE-TX and 100BASE-FX. In the example illustrated in FIG. 7, data terminal equipment (DTE) 1 and data terminal equipment (DTE) 2 each including a 100BASE-TX interface are connected to each other via media converters 3 and 4. The DTE 1 and the media converter 3 are connected to each other by an unshielded twisted pair (UTP) cable 5, and the DTE 2 and the media converter 4 are connected to each other by a UTP cable 6. The media converters 3 and 4 are connected to each other by optical fibers 7A and 7B.
On the other hand, communication apparatuses each provided with a 100BASE-FX interface are directly connected to each other by two optical fibers, one for transmission and the other for reception. Referring to FIG. 8, DTE 8 and DTE 9 each provided with a 100BASE-FX interface are connected to each other by optical fibers 10A and 10B.
100BASE-FX does not support an auto-negotiation function, which is supported by 100BASE-TX. The auto-negotiation function is a function of automatically setting an optimal mode of connection between two connected devices (ports) by performing negotiation regarding communication speeds, communication modes (half-duplex/full-duplex), and the like, between the two connected devices. Hence, when a certain communication apparatus having a 100BASE-FX interface has become unable to receive a signal from a remote communication apparatus, remote fault notification (fault notification) is performed by using a Far-End Fault Indication (FEFI) function instead of using remote fault notification based on the auto-negotiation function.
An FEFI signal is a fault notification signal defined by IEEE 802.3 Clause 24.3.2.1. The FEFI signal is a signal forcibly transmitted irrespective of the data of a media independent interface (MII) when data reception disruption (loss of signal (LOS) of a reception signal) is detected at a 100BASE-FX interface.
FIG. 9 is a general explanatory diagram illustrating the FEFI function. In the example illustrated in FIG. 9, a communication apparatus 11 (on a local station side) including a 100BASE-FX interface apparatus is connected to a communication apparatus 12 (on a remote station side) including a 100BASE-FX interface apparatus by optical fibers 13A and 13B. The communication apparatus 11 receives a signal transmitted from the communication apparatus 12 through the optical fiber 13A, and transmits a signal to the communication apparatus 12 through the optical fiber 13B.
When a fault occurs in the optical fiber 13A (901 in FIG. 9), a signal which is input to the communication apparatus 11 from the communication apparatus 12 stops, and the communication apparatus 11, upon detection of the LOS of the reception signal, starts to output FEFI signals (902 in FIG. 9).
The FEFI signals are continuously transmitted through the optical fiber 13B (903 in FIG. 9). The format of a single FEFI signal is eighty-four “1s” followed by one “0”. The communication apparatus 12, upon detecting three FEFI signals in succession, determines that an abnormality exists (detection of abnormality) in the outgoing line, which is the optical fiber 13A (904 in FIG. 9). As described above, the FEFI function includes the function of generating an FEFI signal upon occurrence of a fault (for example, an LOS due to a link fault) and notifying a remote station of the signal, and the function of detecting a fault through detection of an FEFI signal from the remote apparatus.
A technique of the related art has been disclosed in Japanese Unexamined Patent Application Publication No. 2004-15216.